This study looks at the outcome of Hepatitis B vaccination in prematures and term controls, testing the hypothesis that the T cell activation response to staph endotoxin B will predict the titer of antibody after 9 months. Cord blood is obtained at birth from prematures and a further four samples have been accrued in the past year. Permission to test the response, and to measure the antibody response to Hepatitis B is obtained at follow up. The total number of subjects being followed is currently 36, and the study will be closed to new entrants at this point.